Posted by Soroban on October 28, 2002 at 14:10:43:
In Reply to: pre calc posted by hailey schiller on October 27, 2002 at 20:44:17:
: need help solving the following by subsitution division
: 50x - 18x >0
First, solve the equality: 50x^3 - 18x = 0.
From 2x(25x^2 - 9) = 0, we get x = -3/5, 0, 3/5.
Plot these on a number line, and we have four intervals to consider:
(-oo,-3/5), (-3/5,0), (0,3/5), (3/5,oo)
Test a value from each interval.
For example, on (-3/5,0), try x = -1/2.
We find that 50(-1/2)^3 - 18(-1/2) = 11/4, a positive value.
So, (-3/5,0) is part of the solution.
Do the same test for the other three intervals.
Reject the ones which give a negative value,
keep the ones that give a positive value.
Post a Followup